Maintaining constant and uniform temperatures in livestock buildings in cold-weather climates can be challenging. A majority of livestock buildings utilize unvented LP-gas space heat, operated with on/off control. A few more sophisticated control systems use a combination of a fan speed control and heater control to more closely monitor and control temperatures during periods of minimum ventilation. In the swine industry, supplemental heat is required in farrowing houses, nurseries, and some styles of finishing buildings. In addition, many new facilities are combining nursery and finishing capabilities into a single unit. These buildings also require supplemental heat, depending on time of year and age of the animal.
Winter ventilation rates are kept at a minimum to reduce the amount of supplemental heat required. Therefore, when supplemental heat is required, indoor temperatures tend to rise rapidly to and above the desired set point. The temperature is then allowed to fall below the set point a set amount before the supplemental heat source is reactivated. This prevents rapid repetitive cycling of the supplemental heat source. Unfortunately, this results in significant differences between the high and low room temperature.
High cyclic temperatures can have an adverse effect on swine growth. Combining lighting patterns with temperature control can affect feed intake and pig growth.
Significant research has been devoted to studying the effects of cold and heat stress. The research indicates that both extremes are detrimental to swine growth and performance. Swine tend to huddle together when cold and spread apart when hot. Observing the swine herd in a confinement building allows the operator to determine an appropriate set point. It is also possible to observe periods of apparent heat and cold stress during the temperature swings due to heater operation. Therefore, excessive temperature variation is detrimental to swine performance, especially for immature animals.
One type of climate control which exists is referred to as xe2x80x9con/offxe2x80x9d control. The mode of control is the manner by which a control system makes corrections in response to a disturbance. It relates the operation of the final control element to the measurement information provided by the disturbance-sensing element. On/off control provides only two positions, either full on or full off. There are no intermediate positions. When the controlled variable deviates a predetermined amount from the set point, the final control element moves to either of its extreme positions. The time of travel to on or off is varied according to the load demand.
On/off control is the simplest mode of control, but it has definite disadvantages. It allows the controlled variable to vary over a range instead of letting it settle down to a near-steady condition. If this range becomes too narrow, the controller will rapidly change states, reducing the service life of the controller and the element being controlled.
Multiposition control is an extension of the on/off control to two or more states. When the output range between on to off is too large to achieve the desired response, multiple stages with much smaller ranges can be used. Each stage has only two positions, on or off, but there are as many positions as there are stages, resulting in a step-like operation. The greater the number of stages or steps, the smoother will be the operation. As the demand or load increases, more stages are turned on. Normally, multiposition control provides from two to ten operating stages.
Therefore, the principal object of this invention is to provide a space heater for livestock buildings that is capable of automated variable heat output.
A further object of the invention is to provide a control response as frequently as disturbances occur.
A still further object of the invention is to provide a proportional continuous linear relation between the amount of disturbance, controller action, and position of the final control element.
These and other objects will be apparent to thoses skilled in the art.
A space heater for the interior of a building has a support enclosure containing a gas burner and a gas conduit connecting the burner to a source of combustible gas. An electronically controlled proportional valve is located in the gas conduit. A fan and motor assembly are in the enclosure for distributing heated air from the burner when gas is communicated through the conduit and to the burner for combustion.
A control system and a PC interface of a PC are located in the support enclosure to receive a data processing card having a predetermined temperature set point relating to temperature conditions within the building. A control means comprises a part of the control system and is connected to the PC to be responsive to temperature sensors in the building to cause or cease ignition of gas at the burner when any of the temperature conditions in the building varied with the predetermined temperature set point to permit the production of heat by the burner to automatically bring the varied temperature conditions in the building back towards the temperature of the predetermined temperature set point.